主题：【原创】忽悠一下航母的问题7 -- szbd

只是市井传奇而已。

科学的结论还是要看科学报告，不是演绎故事啊。

At the present day, it is thought that the low weldability of steel was the main cause of the accidents. Furthermore, secondary causes included both the stress concentration due to poor design and initial defect of welding.

Steel experiences ductile fracture at high temperatures and brittle fracture at low temperatures; therefore, steel shows the characteristic of ductile-to-brittle transition. Brittle fracture usually occurs under the conditions of low-temperature, high-loading rate, and multi-axial stress constraint, which can be evaluated by Charpy Impact Test. Absorption energy measured by the test is called the notch toughness. Low notch toughness at low temperature is often the cause of brittle fracture. In other words, notch toughness at low temperature should be high to prevent brittle fracture. The low weldability of steel induces both a reduction of notches toughness at low temperature and weld crack.

The brittle fractures that occurred in the Liberty Ships were caused by low notch toughness at low temperature of steel at welded joint, which started at weld cracks or stress concentration points of the structure. External forces or residual stress due to welding progress the fracture. Almost all accidents by brittle fractures occurred in winter (low temperature). In some cases, residual stress is main cause of fracture, which was typified by the accident of Schenectady ship.